Electroactive polymer motors

ABSTRACT

The present invention relates to mechanical-electrical power conversion systems. The systems comprise one or more electroactive polymers that convert between electrical and mechanical energy. When a voltage is applied to electrodes contacting an electroactive polymer, the polymer deflects. This deflection may be converted into rotation of a power shaft included in a motor. Repeated deflection of the polymer may then produce continuous rotation of the power shaft.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority under U.S.C. §120 from co-pending U.S.patent application Ser. No. 10/090,231, filed Feb. 28, 2002 andentitled, “ELECTROACTIVE POLYMER ROTARY CLUTCH MOTORS”; this patentapplication is incorporated by reference herein for all purposes andclaims priority under 35 U.S.C. § 119(e) from co-pending U.S.Provisional Patent Application No. 60/273,108, which is alsoincorporated by reference for all purposes.

BACKGROUND OF THE INVENTION

The present invention relates generally to motors comprising one or moreelectroactive polymers. More particularly, the present invention relatesto clutch motors and their use in various applications.

A motor converts from an input energy to mechanical energy. Most often,the mechanical energy is output as rotary motion of a shaft, but linearmotors for translating a shaft are also commonly used. The most commonclass of input energy for a motor is electricity. Electric motorsinclude AC, DC, servo, and stepper motors. Compressed air andpressurized hydraulic fluid are also used to power air and hydraulicmotors. Gasoline or diesel engines are another traditional class ofmotors that rely on combustion of a fuel. Each of these motor classeshas advantages and disadvantages that influence their usage.

For a DC motor, DC current is typically supplied from battery sources.Battery voltages are typically in multiples of 1.5 volts, with 12 voltsbeing the most common. DC motors are made in different electricalconfigurations, each of which provides a different torque-speedrelationship that describes how the motor will respond to an appliedload at different speeds. For a permanent magnet DC motor, torque oftenvaries inversely with speed. Since the power available for a DC motor istypically limited, an increase in torque requires a decrease in velocityand vice versa. Thus, when a load is applied, the motor must reducespeed to compensate. One solution to the torque-speed problem is to usea ‘speed-controlled DC motor’, which contains a controller thatincreases and decreases current to the motor in the face of changingload to try and maintain a constant speed. These motors are typicallyexpensive and run from an AC source since the controller converts fromAC to DC.

AC motors provide continuous rotary motion but usually rely on currentsupplied by power companies. They are limited to a few speeds that are afunction of the AC line frequency, e.g., 60 Hz in the U.S. The mostcommon AC motor no-load speeds are 1725 and 3450 revolutions per minute(rpm), which represent some slippage from the more expensive synchronousAC motors speeds of 1800 and 3600 rpm. If other outputs speeds aredesired, a gearbox speed reducer is attached to the motor's outputshaft.

AC and DC motors are designed to provide continuous rotary output.Though they can be stalled against a load, they will not tolerate a fullvoltage, zero velocity stall for an extended period of time withoutoverheating.

Servomotors are fast response, closed loop control motors capable ofproviding a programmed function of acceleration or velocity, or capableof holding a fixed position against a load. Thus, precise positioning ofthe output device is possible, as is control of the speed and shape ofits time response to changes in load or input commands. However, thesedevices are very expensive and are commonly used in applications thatjustify their cost such as moving the flight control services ofaircraft.

Stepper motors are designed to position an output device. Unlikeservomotors, these are typically open loop, meaning they receive nofeedback as to whether the output device has responded as requested.While being relatively good at holding the output in one position forindefinite period, they often are poor with motion and get out of phasewith a desired control. In addition, these motors are moderatelyexpensive, have a low torque capacity, and also require specialcontrollers.

Most electromagnetic motors must consume electrical energy to maintain aforce or torque. The only exceptions would be motors with preferredmagnetic positions such as stepper motors that can resist a torque up tothe torque that causes rotor slippage. But even stepper motors cannotprovide a constant static torque at an arbitrary rotor position unlesspower is used. Thus, conventional electromagnetic motors typically usepower even to hold a static torque where no external work is done. Thisis why at stall and low speed conditions the efficiency of almost allelectromagnetic motors is poor.

Air and hydraulic motors have more limited application than electricmotors since they require the availability of a compressed air orhydraulic source. Both these classes of motors provide poor energyefficiency due to the losses associated with the conversion of energyfirst from chemical or electrical energy to fluid pressure and then tomechanical output. Although individual air motors and air cylinders arerelatively cheap, these pneumatic systems are quite expensive when thecost of all the ancillary equipment is considered.

In addition to the specific drawbacks discussed with respect to eachclass of motor, all of the above motors classes are generally heavy,bulky and not suitable for many applications such as those requiringlight weight continuous output. In view of the foregoing, improvedsystems that convert from an input energy to mechanical energy would bedesirable.

SUMMARY OF THE INVENTION

In one aspect, the present invention relates to a new class of motorsand electrical-mechanical power conversion systems. The systems compriseone or more electroactive polymers that convert between electrical andmechanical energy. When a voltage is applied to electrodes contacting anelectroactive polymer, the polymer deflects. This deflection may beconverted into rotation of a power shaft included in a motor using aclutch. The clutch allows engagement and disengagement between a drivingmember (an electroactive polymer transducer) and a driven member (apower shaft). Repeated deflection of the polymer may then producecontinuous rotation of the power shaft.

Alternatively, when an electroactive polymer deflects, an electric fieldis produced in the polymer. This electric field may be used to produceelectrical energy. Rotation of a power shaft may be used to deflectelectroactive polymer. Continuous rotation of the power shaft made thenbe used to produce continuous electrical energy via the electroactivepolymer.

In another aspect, the present invention relates to amechanical-electrical power conversion system. The system comprises apower shaft configured to rotate about an axis. The system also has atransducer comprising an active area, which includes at least a portionof an electroactive polymer and at least two active area electrodescoupled to the portion of the electroactive polymer. The electroactivepolymer includes pre-strain. The system further comprises a clutch fortransmitting mechanical energy between the transducer and the powershaft, the clutch operably coupled to the power shaft and the transducerin a manner allowing engagement and disengagement of the power shaft tothe transducer.

In yet another aspect, the present invention relates to amechanical-electrical power conversion system. The system comprises apower shaft configured to rotate about an axis. The system alsocomprises a first transducer comprising an active area, which includesat least a portion of a first electroactive polymer and at least twoactive area electrodes coupled to the portion of the first electroactivepolymer. The system further comprises a first clutch for transmittingmechanical energy between the first transducer and the power shaft, thefirst clutch operably coupled to the power shaft and the firsttransducer in a manner allowing engagement and disengagement of thepower shaft to the first transducer. The system additionally comprises asecond transducer comprising an active area, which includes at least aportion of a second electroactive polymer and at least two active areaelectrodes coupled to the portion of the second electroactive polymer.The system also comprises a second clutch for transmitting mechanicalenergy between the second transducer and the power shaft, the secondclutch operably coupled to the power shaft and the second transducer ina manner allowing engagement and disengagement of the power shaft to thesecond transducer.

In still another aspect, the present invention relates to amechanical-electrical power conversion system. The system comprises apower shaft configured to rotate about an axis. The system alsocomprises a transducer comprising an active area, which includes atleast a portion of an electroactive polymer and at least two active areaelectrodes coupled to the portion of the electroactive polymer. Thesystem further comprises a first clutch for transmitting mechanicalenergy between the transducer and the power shaft, the first clutchoperably coupled to the power shaft and the transducer in a mannerallowing engagement and disengagement of the power shaft to thetransducer, the engagement of the first clutch producing rotation of thepower shaft in a first direction about the axis for a first direction ofdeflection of the transducer. The system additionally comprises a secondclutch for transmitting mechanical energy between the transducer and thepower shaft, the second clutch operably coupled to the power shaft andthe transducer in a manner allowing engagement and disengagement of thepower shaft to the transducer, the engagement of the second clutchproducing rotation of the power shaft in the first direction about theaxis for a second direction of deflection of the transducer.

In another aspect, the present invention relates to amechanical-electrical power conversion system. The system comprises apower shaft configured to rotate about an axis. The system alsocomprises a transducer comprising a first active area and a secondactive area. The first active area has at least two first active areaelectrodes and a first portion of the electroactive polymer arranged ina manner which causes the first portion to deflect in response to achange in electric field provided by the at least two first active areaelectrodes. The second active area has at least two second active areaelectrodes and a second portion of the electroactive polymer arranged ina manner which causes the second portion to deflect in response to achange in electric field provided by the at least two second active areaelectrodes. The system additionally comprises a clutch for transmittingmechanical energy between the transducer and the power shaft, the clutchoperably coupled to the power shaft and the transducer in a mannerallowing engagement and disengagement of the power shaft to thetransducer.

In yet another aspect, the present invention relates to a device forconverting between electrical energy and mechanical energy. The devicecomprises at least one transducer. Each transducer has at least twoelectrodes. Each transducer also comprises a polymer arranged in amanner which causes a first portion of the polymer to deflect in thefirst direction in response to a change in electric field and/orarranged in a manner which causes a change in electric field in responseto deflection of the polymer in the first direction. The device furthercomprises a first substantially rigid member attached to a secondportion of the polymer. The device additionally comprises a secondsubstantially rigid member attached to a third portion of the polymer,the second portion and the third portion arranged to increase indistance therebetween upon deflection of the first portion. The devicealso comprises a first flexure coupled to the first and second members,wherein the first flexure improves torsional stiffness for the device.

These and other features and advantages of the present invention will bedescribed in the following description of the invention and associatedfigures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B illustrate a top perspective view of a transducer beforeand after application of a voltage in accordance with one embodiment ofthe present invention.

FIG. 1C illustrates a monolithic transducer comprising a plurality ofactive areas in accordance with one embodiment of the present invention.

FIGS. 2A-2C illustrate a linear actuator suitable for use with motors ofthe present invention.

FIGS. 2D and 2E illustrate a linear actuator suitable for use withmotors of the present invention.

FIG. 2F illustrates cross-sectional side view of a multilayer actuatorfor converting from electrical energy to mechanical energy.

FIGS. 2G-2H illustrate a linear motion device in accordance with oneembodiment of the present invention.

FIG. 2I illustrates a stretched film actuator suitable for use withmotors of the present invention.

FIGS. 2J and 2K illustrate a linear actuator suitable for use withmotors of the present invention.

FIG. 3A illustrates a motor comprising an electroactive polymer inaccordance with one embodiment of the present invention.

FIGS. 3B and 3C illustrate a simplified top view and side view,respectively, of a two clutch motor in accordance with anotherembodiment of the present invention.

FIG. 3D illustrates a simplified top view of a multiple clutch motorincluding four transducers in accordance with another embodiment of thepresent invention.

FIGS. 3E and 3F illustrate a front view and a top view, repsectively, ofa motor in accordance with one embodiment of the present invention.

FIG. 3G illustrates a simplified front view of motor in accordance withanother embodiment of the present invention.

FIG. 3H illustrates a perspective view of motor in accordance withanother embodiment of the present invention.

FIGS. 3I and 3J illustrate a front view and a side perspective view,respectively, of a motor comprising a plurality of active areas on amonolithic transducer in accordance with one embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described in detail with reference toa few preferred embodiments thereof as illustrated in the accompanyingdrawings. In the following description, numerous specific details areset forth in order to provide a thorough understanding of the presentinvention. It will be apparent, however, to one skilled in the art, thatthe present invention may be practiced without some or all of thesespecific details. In other instances, well known process steps and/orstructures have not been described in detail in order to notunnecessarily obscure the present invention.

1. OVERVIEW

In one aspect, the present invention relates to continuous outputsystems that include one or more electroactive polymer transducers. Whenactuated, a transducer of the present invention produces deflection inone or more directions. Repeated actuation of the transducer may producereciprocating motion. Reciprocating motion of a transducer may beconverted to continuous rotary motion of a power shaft included in amotor using a clutch. When engaged, the clutch transmits deflection andpower from an electroactive polymer transducer, a portion thereof, tothe power shaft. A motor in accordance with the present inventioncomprises one or more transducers and clutches configured in aparticular motor design. Combining different ways to configure andconstrain a polymer within a motor, different ways to arrange activeareas on a single or multiple polymers, different motor designs,scalability of electroactive polymers to both micro and macro levels,and different polymer orientations (e.g., rolling or stacking individualpolymer layers) permits a broad range of motors that convert electricalenergy into mechanical power. These motors find use in a wide range ofapplications.

For ease of understanding, the present invention is mainly described andshown by focusing on a single direction of energy conversion. Morespecifically, the present invention focuses on converting electricalenergy into mechanical energy. The mechanical energy is most oftendescribed herein as continuous rotary output power or rotary output fora number of polymer deflections. However, in all the figures anddiscussions for the present invention, it is important to note that thepolymers and systems may convert between electrical energy andmechanical energy bi-directionally. Thus, any of the electroactivepolymer systems and motor designs described herein also convertmechanical energy to electrical energy (generator mode) by oscillatingthe shaft input though an angle. Typically, a generator of the presentinvention comprises a polymer arranged in a manner that causes a changein electric field in response to deflection of a portion of the polymer.The change in electric field, along with changes in the polymerdimension in the direction of the field, produces a change in voltage,and hence a change in electrical energy.

For a transducer having a substantially constant thickness, onemechanism for differentiating the performance of the transducer, or aportion of the transducer associated with a single active area, as beingan actuator or a generator is in the change in net area orthogonal tothe thickness associated with the polymer deflection. For thesetransducers or active areas, when the deflection causes the net area ofthe transducer/active area to decrease and there is charge on theelectrodes, the transducer/active area is converting from mechanical toelectrical energy and acting as a generator. Conversely, when thedeflection causes the net area of the transducer/active area to increaseand charge is on the electrodes; the transducer/active area isconverting electrical to mechanical energy and acting as an actuator.The change in area in both cases corresponds to a reverse change in filmthickness, i.e., the thickness contracts when the planar area expands,and the thickness expands when the planar area contracts. Both thechange in area and change in thickness affect the amount of energy thatis converted between electrical and mechanical. Since the effects due toa change in area and corresponding change in thickness arecomplementary, only the change in area will be discussed herein for sakeof brevity. In addition, although deflection of an electroactive polymerwill primarily be discussed as a net increase in area of the polymerwhen the polymer is being used in an actuator to produce mechanicalenergy, it is understood that in some cases (i.e. depending on theloading), the net area may decrease to produce mechanical work.Alternatively, when an electroactive polymer is continuously beingcycled between actuator and generator modes, electrical or mechanical(elastic) energy may be stored from one part of the cycle for use inother parts of the cycle. This may further introduce situations in whichthe net area may decrease to produce mechanical work. Thus, devices ofthe present invention may include both actuator and generator modes,depending on how the polymer is arranged and applied.

2. GENERAL STRUCTURE OF ELECTROACTIVE POLYMERS

The transformation between electrical and mechanical energy in devicesof the present invention is based on energy conversion of one or moreactive areas of an electroactive polymer. Electroactive polymers deflectwhen actuated by electrical energy. To help illustrate the performanceof an electroactive polymer in converting electrical energy tomechanical energy, FIG. 1A illustrates a top perspective view of atransducer portion 100 in accordance with one embodiment of the presentinvention. The transducer portion 100 comprises an electroactive polymer102 for converting between electrical energy and mechanical energy. Inone embodiment, an electroactive polymer refers to a polymer that actsas an insulating dielectric between two electrodes and may deflect uponapplication of a voltage difference between the two electrodes. Top andbottom electrodes 104 and 106 are attached to the electroactive polymer102 on its top and bottom surfaces, respectively, to provide a voltagedifference across a portion of the polymer 102. Polymer 102 deflectswith a change in electric field provided by the top and bottomelectrodes 104 and 106. Deflection of the transducer portion 100 inresponse to a change in electric field provided by the electrodes 104and 106 is referred to as actuation. As polymer 102 changes in size, thedeflection may be used to produce mechanical work.

FIG. 1B illustrates a top perspective view of the transducer portion 100including deflection in response to a change in electric field. Ingeneral, deflection refers to any displacement, expansion, contraction,torsion, linear or area strain, or any other deformation of a portion ofthe polymer 102. The change in electric field corresponding to thevoltage difference applied to or by the electrodes 104 and 106 producesmechanical pressure within polymer 102. In this case, the unlikeelectrical charges produced by electrodes 104 and 106 attract each otherand provide a compressive force between electrodes 104 and 106 and anexpansion force on polymer 102 in planar directions 108 and 110, causingpolymer 102 to compress between electrodes 104 and 106 and stretch inthe planar directions 108 and 110.

In some cases, electrodes 104 and 106 cover a limited portion of polymer102 relative to the total area of the polymer. This may be done toprevent electrical breakdown around the edge of polymer 102 or toachieve customized deflections for one or more portions of the polymer.As the term is used herein, an active area is defined as a portion of atransducer comprising polymer material 102 and at least two electrodes.When the active area is used to convert electrical energy to mechanicalenergy, the active area includes a portion of polymer 102 havingsufficient electrostatic force to enable deflection of the portion. Whenthe active area is used to convert mechanical energy to electricalenergy, the active area includes a portion of polymer 102 havingsufficient deflection to enable a change in electrostatic energy. Aswill be described below, a polymer of the present invention may havemultiple active areas. In some cases, polymer 102 material outside anactive area may act as an external spring force on the active areaduring deflection. More specifically, polymer material outside theactive area may resist active area deflection by its elastic contractionor expansion. Removal of the voltage difference and the induced chargecauses the reverse effects.

Electrodes 104 and 106 are compliant and change shape with polymer 102.The configuration of polymer 102 and electrodes 104 and 106 provides forincreasing polymer 102 response with deflection. More specifically, asthe transducer portion 100 deflects, compression of polymer 102 bringsthe opposite charges of electrodes 104 and 106 closer and the stretchingof polymer 102 separates similar charges in each electrode. In oneembodiment, one of the electrodes 104 and 106 is ground.

In general, the transducer portion 100 continues to deflect untilmechanical forces balance the electrostatic forces driving thedeflection. The mechanical forces include elastic restoring forces ofthe polymer 102 material, the compliance of electrodes 104 and 106, andany external resistance provided by a device and/or load coupled to thetransducer portion 100, etc. The deflection of the transducer portion100 as a result of the applied voltage may also depend on a number ofother factors such as the polymer 102 dielectric constant and the sizeof polymer 102.

Electroactive polymers in accordance with the present invention arecapable of deflection in any direction. After application of the voltagebetween the electrodes 104 and 106, the electroactive polymer 102increases in size in both planar directions 108 and 110. In some cases,the electroactive polymer 102 is incompressible, e.g. has asubstantially constant volume under stress. In this case, the polymer102 decreases in thickness as a result of the expansion in the planardirections 108 and 110. It should be noted that the present invention isnot limited to incompressible polymers and deflection of the polymer 102may not conform to such a simple relationship.

Application of a relatively large voltage difference between electrodes104 and 106 on the transducer portion 100 shown in FIG. 1A will causetransducer portion 100 to change to a thinner, larger area shape asshown in FIG. 1B. In this manner, the transducer portion 100 convertselectrical energy to mechanical energy. The transducer portion 100 mayalso be used to convert mechanical energy to electrical energy.

FIGS. 1A and 1B may be used to show one manner in which the transducerportion 100 converts mechanical energy to electrical energy. Forexample, if the transducer portion 100 is mechanically stretched byexternal forces to a thinner, larger area shape such as that shown inFIG. 1B, and a relatively small voltage difference (less than thatnecessary to actuate the film to the configuration in FIG. 1B) isapplied between electrodes 104 and 106, the transducer portion 100 willcontract in area between the electrodes to a shape such as in FIG. 1Awhen the external forces are removed. Stretching the transducer refersto deflecting the transducer from its original restingposition—typically to result in a larger net area between theelectrodes, e.g. in the plane defined by directions 108 and 110 betweenthe electrodes. The resting position refers to the position of thetransducer portion 100 having no external electrical or mechanical inputand may comprise any pre-strain in the polymer. Once the transducerportion 100 is stretched, the relatively small voltage difference isprovided such that the resulting electrostatic forces are insufficientto balance the elastic restoring forces of the stretch. When theexternal forces are removed, the transducer portion 100 thereforecontracts, and it becomes thicker and has a smaller planar area in theplane defined by directions 108 and 110 (orthogonal to the thicknessbetween electrodes). When polymer 102 becomes thicker, it separateselectrodes 104 and 106 and their corresponding unlike charges, thusraising the electrical energy and voltage of the charge. Further, whenelectrodes 104 and 106 contract to a smaller area, like charges withineach electrode compress, also raising the electrical energy and voltageof the charge. Thus, with different charges on electrodes 104 and 106,contraction from a shape such as that shown in FIG. 1B to one such asthat shown in FIG. 1A raises the electrical energy of the charge. Thatis, mechanical deflection is being turned into electrical energy and thetransducer portion 100 is acting as a generator.

In some cases, the transducer portion 100 may be described electricallyas a variable capacitor. The capacitance decreases for the shape changegoing from that shown in FIG. 1B to that shown in FIG. 1A. Typically,the voltage difference between electrodes 104 and 106 will be raised bycontraction. This is normally the case, for example, if additionalcharge is not added or subtracted from electrodes 104 and 106 during thecontraction process. The increase in electrical energy, U, may beillustrated by the formula U=0.5 Q²/C, where Q is the amount of positivecharge on the positive electrode and C is the variable capacitance whichrelates to the intrinsic dielectric properties of polymer 102 and itsgeometry. If Q is fixed and C decreases, then the electrical energy Uincreases. The increase in electrical energy and voltage can berecovered or used in a suitable device or electronic circuit inelectrical communication with electrodes 104 and 106. In addition, thetransducer portion 100 may be mechanically coupled to a mechanical inputthat deflects the polymer and provides mechanical energy.

The transducer portion 100 will convert mechanical energy to electricalenergy when it contracts. Some or all of the charge and energy can beremoved when the transducer portion 100 is fully contracted in the planedefined by directions 108 and 110. Alternatively, some or all of thecharge and energy can be removed during contraction. If the electricfield pressure in the polymer increases and reaches balance with themechanical elastic restoring forces and external load duringcontraction, the contraction will stop before full contraction, and nofurther elastic mechanical energy will be converted to electricalenergy. Removing some of the charge and stored electrical energy reducesthe electrical field pressure, thereby allowing contraction to continue.Thus, removing some of the charge may further convert mechanical energyto electrical energy. The exact electrical behavior of the transducerportion 100 when operating as a generator depends on any electrical andmechanical loading as well as the intrinsic properties of polymer 102and electrodes 104 and 106.

In one embodiment, electroactive polymer 102 is pre-strained. Pre-strainof a polymer may be described, in one or more directions, as the changein dimension in a direction after pre-straining relative to thedimension in that direction before pre-straining. The pre-strain maycomprise elastic deformation of polymer 102 and be formed, for example,by stretching the polymer in tension and fixing one or more of the edgeswhile stretched. For many polymers, pre-strain improves conversionbetween electrical and mechanical energy. The improved mechanicalresponse enables greater mechanical work for an electroactive polymer,e.g., larger deflections and actuation pressures. In one embodiment,prestrain improves the dielectric strength of the polymer. In anotherembodiment, the pre-strain is elastic. After actuation, an elasticallypre-strained polymer could, in principle, be unfixed and return to itsoriginal state. The pre-strain may be imposed at the boundaries using arigid frame or may also be implemented locally for a portion of thepolymer.

In one embodiment, pre-strain is applied uniformly over a portion ofpolymer 102 to produce an isotropic pre-strained polymer. For example,an acrylic elastomeric polymer may be stretched by 200 to 400 percent inboth planar directions. In another embodiment, pre-strain is appliedunequally in different directions for a portion of polymer 102 toproduce an anisotropic pre-strained polymer. In this case, polymer 102may deflect greater in one direction than another when actuated. Whilenot wishing to be bound by theory, it is believed that pre-straining apolymer in one direction may increase the stiffness of the polymer inthe pre-strain direction. Correspondingly, the polymer is relativelystiffer in the high pre-strain direction and more compliant in the lowpre-strain direction and, upon actuation, more deflection occurs in thelow pre-strain direction. In one embodiment, the deflection in direction108 of transducer portion 100 can be enhanced by exploiting largepre-strain in the perpendicular direction 110. For example, an acrylicelastomeric polymer used as the transducer portion 100 may be stretchedby 100 percent in direction 108 and by 500 percent in the perpendiculardirection 110. The quantity of pre-strain for a polymer may be based onthe polymer material and the desired performance of the polymer in anapplication. Pre-strain suitable for use with the present invention isfurther described in copending U.S. patent application Ser. No.09/619,848, which is incorporated by reference for all purposes.

Generally, after the polymer is pre-strained, it may be fixed to one ormore objects. Each object is preferably suitably stiff to maintain thelevel of pre-strain desired in the polymer. The polymer may be fixed tothe one or more objects according to any conventional method known inthe art such as a chemical adhesive, an adhesive layer or material,mechanical attachment, etc.

Transducers and pre-strained polymers of the present invention are notlimited to any particular geometry or type of deflection. For example,the polymer and electrodes may be formed into any geometry or shapeincluding tubes and rolls, stretched polymers attached between multiplerigid structures, stretched polymers attached across a frame of anygeometry—including curved or complex geometries, across a frame havingone or more joints, etc. Deflection of a transducer according to thepresent invention includes linear expansion and compression in one ormore directions, bending, axial deflection when the polymer is rolled,deflection out of a hole provided on a substrate, etc. Deflection of atransducer may be affected by how the polymer is constrained by a frameor rigid structures attached to the polymer. In one embodiment, aflexible material that is stiffer in elongation than the polymer isattached to one side of a transducer to induce bending when the polymeris actuated.

Materials suitable for use as a pre-strained polymer with the presentinvention may include any substantially insulating polymer or rubber (orcombination thereof) that deforms in response to an electrostatic forceor whose deformation results in a change in electric field. One suitablematerial is NuSil CF 19-2186 as provided by NuSil Technology ofCarpenteria, Calif. Other exemplary materials suitable for use as apre-strained polymer include silicone elastomers, acrylic elastomerssuch as VHB 4910 acrylic elastomer as produced by 3M Corporation of St.Paul, Minn., polyurethanes, thermoplastic elastomers, copolymerscomprising PVDF, pressure-sensitive adhesives, fluoroelastomers,polymers comprising silicone and acrylic moieties, and the like.Polymers comprising silicone and acrylic moieties may include copolymerscomprising silicone and acrylic moieties, polymer blends comprising asilicone elastomer and an acrylic elastomer, for example. Combinationsof some of these materials may also be used as the electroactive polymerin transducers of this invention.

An electroactive polymer layer in transducers of the present inventionmay have a wide range of thicknesses. In one embodiment, polymerthickness may range between about 1 micrometer and 2 millimeters.Polymer thickness may be reduced by stretching the film in one or bothplanar directions. In many cases, electroactive polymers of the presentinvention may be fabricated and implemented as thin films. Thicknessessuitable for these thin films may be below 50 micrometers.

Although the discussion so far has focused primarily on one type ofelectroactive polymer commonly referred to as dielectric elastomers(transducer 100 of FIG. 1A), motors of the present invention may alsoincorporate other conventional electroactive polymers. As the term isused herein, an electroactive polymer refers to a polymer that respondsto electrical stimulation. Other common classes of electroactive polymersuitable for use with many embodiments of the present invention includeelectrostrictive polymers, electronic electroactive polymers, and ionicelectroactive polymers, and some copolymers. Electrostrictive polymersare characterized by the non-linear reaction of a electroactive polymers(relating strain to E²). Electronic electroactive polymers typicallychange shape or dimensions due to migration of electrons in response toelectric field (usually dry). Ionic electroactive polymers are polymersthat change shape or dimensions due to migration of ions in response toelectric field (usually wet and contains electrolyte). Irradiatedcopolymer of polyvinylidene difluoride and trifluoroethelene P(VDF-TrFE)is an electroactive polymer suitable for use with some embodiments ofthe present invention.

Suitable actuation voltages for electroactive polymers, or portionsthereof, may vary based on the material properties of the electroactivepolymer, such as the dielectric constant, as well as the dimensions ofthe polymer, such as the thickness of the polymer film. For example,actuation electric fields used to actuate polymer 102 in FIG. 1A mayrange in magnitude from about 0 V/m to about 440 MV/m. Actuationelectric fields in this range may produce a pressure in the range ofabout 0 Pa to about 10 MPa. In order for the transducer to producegreater forces, the thickness of the polymer layer may be increased.Actuation voltages for a particular polymer may be reduced by increasingthe dielectric constant, decreasing the polymer thickness, anddecreasing the modulus of elasticity, for example.

As electroactive polymers of the present invention may deflect at highstrains, electrodes attached to the polymers should also deflect withoutcompromising mechanical or electrical performance. Generally, electrodessuitable for use with the present invention may be of any shape andmaterial provided that they are able to supply a suitable voltage to, orreceive a suitable voltage from, an electroactive polymer. The voltagemay be either constant or varying over time. In one embodiment, theelectrodes adhere to a surface of the polymer. Electrodes adhering tothe polymer are preferably compliant and conform to the changing shapeof the polymer. Correspondingly, the present invention may includecompliant electrodes that conform to the shape of an electroactivepolymer to which they are attached. The electrodes may be only appliedto a portion of an electroactive polymer and define an active areaaccording to their geometry. Several examples of electrodes that onlycover a portion of an electroactive polymer will be described in furtherdetail below.

Various types of electrodes suitable for use with the present inventionare described in copending U.S. patent application Ser. No. 09/619,848,which was previously incorporated by reference above. Electrodesdescribed therein and suitable for use with the present inventioninclude structured electrodes comprising metal traces and chargedistribution layers, textured electrodes comprising varying out of planedimensions, conductive greases such as carbon greases or silver greases,colloidal suspensions, high aspect ratio conductive materials such ascarbon fibrils and carbon nanotubes, and mixtures of ionicallyconductive materials.

Materials used for electrodes of the present invention may vary.Suitable materials used in an electrode may include graphite, carbonblack, colloidal suspensions, thin metals including silver and gold,silver filled and carbon filled gels and polymers, and ionically orelectrically conductive polymers. In a specific embodiment, an electrodesuitable for use with the present invention comprises 80 percent carbongrease and 20 percent carbon black in a silicone rubber binder such asStockwell RTV60-CON as produced by Stockwell Rubber Co. Inc. ofPhiladelphia, Pa. The carbon grease is of the type such as NyoGel 756Gas provided by Nye Lubricant Inc. of Fairhaven, Mass. The conductivegrease may also be mixed with an elastomer, such as silicon elastomerRTV 118 as produced by General Electric of Waterford, N.Y., to provide agel-like conductive grease.

It is understood that certain electrode materials may work well withparticular polymers and may not work as well for others. For example,carbon fibrils work well with acrylic elastomer polymers while not aswell with silicone polymers. For most transducers, desirable propertiesfor the compliant electrode may include one or more of the following:low modulus of elasticity, low mechanical damping, low surfaceresistivity, uniform resistivity, chemical and environmental stability,chemical compatibility with the electroactive polymer, good adherence tothe electroactive polymer, and the ability to form smooth surfaces. Insome cases, a transducer of the present invention may implement twodifferent types of electrodes, e.g. a different electrode type for eachactive area or different electrode types on opposing sides of a polymer.

Electronic drivers are typically connected to the electrodes. Thevoltage provided to electroactive polymer will depend upon specifics ofan application. In one embodiment, a transducer of the present inventionis driven electrically by modulating an applied voltage about a DC biasvoltage. Modulation about a bias voltage allows for improved sensitivityand linearity of the transducer to the applied voltage. For example, atransducer used in an audio application may be driven by a signal of upto 200 to 1000 volts peak to peak on top of a bias voltage ranging fromabout 750 to 2000 volts DC.

3. MULTIPLE ACTIVE AREAS

In accordance with the present invention, the term “monolithic” is usedherein to refer to electroactive polymers, transducers, and devicescomprising a plurality of active areas.

FIG. 1C illustrates a monolithic transducer 150 comprising a pluralityof active areas in accordance with one embodiment of the presentinvention. The monolithic transducer 150 converts between electricalenergy and mechanical energy. The monolithic transducer 150 comprises anelectroactive polymer 151 including two active areas 152 a and 152 b.The polymer 151 can be held using, for example, a rigid frame (notshown) attached at the edges of the polymer 151.

The active area 152 a has top and bottom electrodes 154 a and 154 battached to the polymer 151 on its top and bottom surfaces 151 c and 151d, respectively. The electrodes 154 a and 154 b provide a voltagedifference across a portion 151 a of the polymer 151. The portion 151 adeflects with a change in electric field provided by the electrodes 154a and 154 b. The portion 151 a comprises the polymer 151 between theelectrodes 154 a and 154 b and any other portions of the polymer 151having sufficient electrostatic force to enable deflection uponapplication of voltages using the electrodes 154 a and 154 b. When thedevice 150 is used as a generator to convert from electrical energy tomechanical energy, deflection of the portion 151 a causes a change inelectric field in the portion 151 a that is received as a change involtage difference by the electrodes 154 a and 154 b.

The active area 152 b has top and bottom electrodes 156 a and 156 battached to the polymer 151 on its top and bottom surfaces 151 c and 151d, respectively. The electrodes 156 a and 156 b provide a voltagedifference across a portion 151 b of the polymer 151. The portion 151 bdeflects with a change in electric field provided by the electrodes 156a and 156 b. The portion 151 b comprises the polymer 151 between theelectrodes 156 a and 156 b and any other portions of the polymer 151having sufficient stress induced by the electrostatic force to enabledeflection upon application of voltages using the electrodes 156 a and156 b. When the device 150 is used as a generator to convert fromelectrical energy to mechanical energy, deflection of the portion 151 bcauses a change in electric field in the portion 151 b that is receivedas a change in voltage difference by the electrodes 156 a and 156 b.

The active areas for monolithic polymers and transducers of the presentinvention may be flexibly arranged. In one embodiment, active areas in apolymer are arranged such that elasticity of the active areas isbalanced. In another embodiment, a transducer of the present inventionincludes a plurality of symmetrically arranged active areas. Furtherdescription of monolithic transducers suitable for use with the presentinvention are further described in commonly owned U.S. Pat. No.6,664,718, which is incorporated by reference herein for all purposes.

4. ACTUATOR DESIGNS

The deflection of an electroactive polymer can be used in a variety ofways to produce or receive mechanical energy. One common implementationof a transducer in a motor is within an actuator. Several exemplaryactuators suitable for use with motors of the present invention will nowbe discussed.

Expansion in one direction of an electroactive polymer may inducecontractile stresses in a second direction such as due to Poissoneffects. This may reduce the mechanical output for a transducer thatprovides mechanical output in the second direction. Correspondingly,actuators used in motors of the present invention may be designed toconstrain a polymer in the non-output direction. In some cases,actuators may be designed to improve mechanical output using deflectionin the non-output direction.

An actuator that uses deflection in one planar direction to improveenergy conversion in the other planar direction is a bow actuator. FIGS.2A and 2B illustrate a bow actuator 200 suitable for use with motors ofthe present invention. The bow actuator 200 is a planar mechanismcomprising a flexible frame 202 which provides mechanical assistance toimprove conversion from electrical energy to mechanical energy for apolymer 206 attached to the frame 202. The frame 202 includes six rigidmembers 204 connected at joints 205. The members 204 and joints 205provide mechanical assistance by coupling polymer deflection in a planardirection 208 into mechanical output in a perpendicular planar direction210. More specifically, the frame 202 is arranged such that a smalldeflection of the polymer 206 in the direction 208 improves displacementin the perpendicular planar direction 210. Attached to opposing (top andbottom) surfaces of the polymer 206 are electrodes 207 (bottom electrodeon bottom side of polymer 206 not shown) to provide a voltage differenceacross a portion of the polymer 206.

The polymer 206 is configured with different levels of pre-strain in itsorthogonal directions. More specifically, electroactive polymer 206includes a high pre-strain in the planar direction 208, and little or nopre-strain in the perpendicular planar direction 210. This anisotropicpre-strain is arranged relative to the geometry of the frame 202. Morespecifically, upon actuation using electrodes 207, the polymer contractsin the high pre-strained direction 208. With the restricted motion ofthe frame 202 and the lever arm provided by the members 204, thiscontraction helps drive deflection in the perpendicular planar direction210. Thus, even for a short deflection of the polymer 206 in the highpre-strain direction 208, the frame 202 bows outward in the direction210. In this manner, a small contraction in the high pre-straindirection 210 becomes a larger expansion in the relatively lowpre-strain direction 208.

Using the anisotropic pre-strain and constraint provided by the frame202, the bow actuator 200 allows contraction in one direction to enhancemechanical deflection and electrical to mechanical conversion inanother. In other words, a load 211 (FIG. 2B) attached to the bowactuator 200 is coupled to deflection of the polymer 206 in twodirections—direction 208 and 210. Thus, as a result of the differentialpre-strain of the polymer 206 and the geometry of the frame 202, the bowactuator 200 is able to provide a larger mechanical displacement andmechanical energy output than an electroactive polymer alone for commonelectrical input.

The pre-strain in the polymer 206 and constraint provided by the frame202 may also allow the bow actuator 200 to use lower actuation voltagesfor the pre-strained polymer 206 for a given deflection. As the bowactuator 200 has a lower effective modulus of elasticity in the lowpre-strained direction 210, the mechanical constraint provided by theframe 202 allows the bow actuator 200 to be actuated in the direction210 to a larger deflection with a lower voltage. In addition, the highpre-strain in the direction 208 increases the breakdown strength of thepolymer 206, permitting higher voltages and higher deflections for thebow actuator 200.

In one embodiment, the bow actuator 200 may include additionalcomponents to provide mechanical assistance and enhance deflection. Byway of example, springs 220 as shown in FIG. 2C may be attached to thebow actuator 200 to enhance deflection in the direction 210. The springsload the bow actuator 200 such that the spring force exerted by thesprings 220 opposes resistance provided by an external load. In somecases, the springs 220 provide increasing assistance for bow actuator200 deflection. In addition, pre-strain may be increased to enhancedeflection. The load may also be coupled to the rigid members 204 on topand bottom of the frame 202 rather than on the rigid members of the sideof the frame 202 (as shown in FIG. 2B).

The shape and constraint of an electroactive polymer may affectdeflection. An aspect ratio for an electroactive polymer is defined asthe ratio of its length to width. If the aspect ratio is high (e.g., anaspect ratio of at least about 4:1) and the polymer is constrained alongits length by rigid members, than the combination may result in asubstantially one-dimensional deflection in the width direction.

FIGS. 2D and 2E illustrate a linear motion actuator 230 suitable for usewith motors of the present invention. Linear motion actuator 230 is aplanar mechanism having mechanical deflection in one direction. Linearmotion actuator 230 comprises a polymer 231 having a length 233substantially greater than its width 234 (e.g., an aspect ratio at leastabout 4:1). Polymer 231 is attached on opposite sides to stiff members232 of a frame along its length 233. Stiff members 232 have a greaterstiffness than the polymer 231. The geometric edge constraint providedby stiff members 232 substantially prevents displacement in a direction236 along the polymer length 233 and facilitates deflection almostexclusively in a direction 235. When the linear motion actuator 230 isimplemented with a polymer 231 having anisotropic pre-strain, such as ahigher pre-strain in the direction 236 than in the direction 235, thenthe polymer 231 is stiffer in the direction 236 than in the direction235 and large deflections in the direction 235 may result.

A collection of electroactive polymers or actuators may be mechanicallylinked to form a larger actuator with a common output, e.g. force and/ordisplacement. By using a small electroactive polymer as a base unit in acollection, conversion of electric energy to mechanical energy may bescaled according to an application. By way of example, multiple linearmotion actuators 230 may be combined in series in the direction 235 toform an actuator having a cumulative deflection of all the linear motionactuators in the series.

FIG. 2F illustrates cross-sectional side view of a multilayer actuator240 for converting from electrical energy to mechanical energy. Themultilayer actuator 240 includes four pre-strained polymers 241 arrangedin parallel and each attached to a rigid frame 242 such that they havethe same deflection. Electrodes 243 and 244 are deposited on oppositesurfaces of each polymer 241 and provide simultaneous electrostaticactuation to the four pre-strained polymers 241. The multilayer actuator240 provides cumulative force output of the individual polymer layers241.

An electroactive polymer is typically compliant and does not provide alarge stiffness, e.g., relative to a solid structure. Many mechanicalapplications require an electroactive polymer actuator having stiffnessin all directions but the direction of actuation. Rigid members may beincluded in a device and provide stiffness in one or more directions.However, these stiff members may constrain deflection of the polymer andare typically not used in the direction of output motion.

FIG. 2G illustrates a linear motion device 350 in accordance with oneembodiment of the present invention. The device 350 is a planarmechanism having mechanical deflection in one direction 351. The device350 comprises an electroactive polymer 352 arranged in a manner whichcauses a portion of the polymer to deflect in response to a change inelectric field. Electrodes 360 a and 360 b are attached to oppositesurfaces (only the foremost electrode 360 a is shown) of the polymer 352and cover a substantial portion of the polymer 352. The polymer 352 isattached to a frame 353. The frame 353 provides mechanical support andstiffness for the device 350 in all directions, linear and torsional,except a direction of output motion 359 b. The frame 353 includes stiffmembers 354 and 355 each connected to distal ends of flexures 357 and358.

The stiff members 354 and 355 are attached along opposite edges 352 aand 352 b, respectively, of the polymer 352. The stiff members 354 and355 have a greater stiffness than the polymer 352. The added stiffnessand geometric constraint provided by the stiff members 354 and 355substantially prevents displacement in a direction 359 a along thepolymer length. Using only the stiff members, compliance for the device350 remains in the direction 351 and any torsional deflection about thepolymer 352.

Upon actuation of the polymer 352, expansion of the polymer 352 in thedirection 351 causes edges 352 a and 352 b and the stiff members 354 and355 to move apart, as shown in FIG. 2H. In addition, expansion of thepolymer 352 in the direction 351 causes the torsional supports 357 and358 to straighten. Thus, deflection of the device 350 is almostexclusively in the direction 351.

Flexures 357 and 358 provide torsional stiffness for the device 350.Without flexures 357 and 358, the stiff members 354 and 355 may twistout of the plane of the polymer 352. In one embodiment, each flexure 357and 358 is a two-bar linkage. For example, the flexure 357 comprisesfirst and second members 361 and 362 hingeably coupled to each other attheir proximate ends 361 a and 362 a, respectively. The first and secondmembers 361 and 362 are also hingeably coupled to the stiff members 354and 355 at their distal ends 361 b and 362 b, respectively. The firstand second members 361 and 362 prevent torsion about the axis 351 butallow deflection of the device linearly in the direction 359 b.

One advantage of the device 350 is that the entire structure is planar.This allows for easy mechanical coupling and simple expansion to producemultiple polymer designs. By way of example, the stiff members 354 and355 may be mechanically coupled (e.g. glued or similarly fixed) to theirrespective counterparts of a second device 350 to provide two devices350 in parallel in order to increase the force output over a singledevice 350. Similarly, the stiff member 354 from one device may beattached to the stiff member 355 from a second device in order toprovide multiple actuators in series that increase the deflection outputover a single device 350.

The constraint and shape of an electroactive polymer may affectdeflection. In one embodiment, the polymer 352 has a length (along thedimension 359 b) substantially greater than its width (along thedimension 359 a). In a specific embodiment, the polymer has an aspectratio at least about 4:1. In another embodiment, the device 350 isimplemented with a polymer 352 having anisotropic pre-strain. Forexample, the polymer may include a higher pre-strain in the direction359 a than the direction 359 b. As a result, the polymer 352 is stifferin the direction 359 a than the direction 359 b and larger deflectionsin the direction 359 b may result during actuation when voltage isapplied to the electrodes 360.

In another embodiment, electroactive polymers suitable for use withmotors of the present invention may be rolled or folded into lineartransducers and actuators that deflect axially while converting fromelectrical energy to mechanical energy. As fabrication of electroactivepolymers is often simplest with fewer numbers of layers, rolledactuators provide an efficient manner of squeezing large layers ofpolymer into a compact shape. Rolled or folded transducers and actuatorstypically include two or more layers of polymer. Rolled or foldedactuators are applicable wherever linear actuators are used, such asrobotic legs and fingers, high force grippers, or any of the motordesigns described below.

FIG. 2I illustrates a stretched film actuator 270 suitable for use withmotors of the present invention. The stretched film actuator 270includes a rigid frame 271 having a hole 272. An electroactive polymer273 is attached in tension to the frame 271 and spans the hole 272. Arigid bar 274 is attached to the center of the polymer 273 and providesexternal displacement corresponding to deflection of the polymer 273.Compliant electrode pairs 275 and 276 are patterned on both top andbottom surfaces of the polymer 273 on the left and right sidesrespectively of the rigid bar 274.

When the electrode pair 275 is actuated, a portion of the polymer 273between and in the vicinity of the top and bottom electrode pair 275expands relative to the rest of the polymer 273 and the existing tensionin the remainder of the polymer 273 pulls the rigid bar 274 to move tothe right. Conversely, when the electrode pair 276 is actuated, a secondportion of the polymer 273 affected by the electrode pair 276 expandsrelative to the rest of the polymer 273 and allows the rigid bar 274 tomove to the left. Alternating actuation of the electrodes 275 and 276provides a total stroke 279 for the rigid bar 274. One variation of thisactuator includes adding anisotropic pre-strain to the polymer such thatthe polymer has high pre-strain (and stiffness) in the directionperpendicular to the rigid bar displacement. Another variation is toeliminate one of the electrode pairs. For the benefit of simplifying thedesign, this variation reduces the stroke 279 for the stretched filmactuator 270. In this case, the portion of the polymer no longer used bythe removed electrode now responds passively like a restoring spring.

FIGS. 2J and 2K illustrate an actuator 300 suitable for use in motors ofthe present invention. The actuator 300 includes a polymer 302 arrangedin a manner which causes a portion of the polymer to deflect in responseto a change in electric field. Electrodes 304 are attached to oppositesurfaces (only the foremost electrode is shown) of the polymer 302 andcover a substantial portion of the polymer 302. Two stiff members 308and 310 extend along opposite edges 312 and 314 of the polymer 302.Flexures 316 and 318 are situated along the remaining edges of thepolymer 302. The flexures 316 and 318 improve conversion from electricalenergy to mechanical energy for the actuator 300.

The flexures 316 and 318 couple polymer 302 deflection in one directioninto deflection in another direction. In one embodiment, each of theflexures 316 and 318 rest at an angle about 45 degrees in the plane ofthe polymer 302. Upon actuation of the polymer 302, expansion of thepolymer 302 in the direction 320 causes the stiff members 308 and 310 tomove apart, as shown in FIG. 20. In addition, expansion of the polymer302 in the direction 322 causes the flexures 316 and 318 to straighten,and further separates the stiff members 308 and 310. In this manner, theactuator 300 couples expansion of the polymer 302 in both planardirections 320 and 322 into mechanical output in the direction 320.

The polymer 302 is configured with different levels of pre-strain inorthogonal directions 320 and 322. This anisotropic pre-strain isarranged relative to the geometry of the flexures 316 and 318. Morespecifically, the polymer 302 includes a higher pre-strain in thedirection 320, and little or no pre-strain in the perpendicular planardirection 322.

FIGS. 2J and 2K illustrate a linear actuator 300 suitable for use withmotors of the present invention. The actuator 300 includes a polymer 302arranged in a manner which causes a portion of the polymer to deflect inresponse to a change in electric field. Electrodes 304 are attached toopposite surfaces (only the foremost electrode is shown) of the polymer302 and cover a substantial portion of the polymer 302. Two stiffmembers 308 and 310 extend along opposite edges 312 and 314 of thepolymer 302. Flexures 316 and 318 are situated along the remaining edgesof the polymer 302. The flexures 316 and 318 improve conversion fromelectrical energy to mechanical energy for the actuator 300.

The flexures 316 and 318 couple polymer 302 deflection in one directioninto deflection in another direction. In one embodiment, each of theflexures 316 and 318 rest at an angle about 45 degrees in the plane ofthe polymer 302. Upon actuation of the polymer 302, expansion of thepolymer 302 in the direction 320 causes the stiff members 308 and 310 tomove apart, as shown in FIG. 2E. In addition, expansion of the polymer302 in the direction 322 causes the flexures 316 and 318 to straighten,and further separates the stiff members 308 and 310. In this manner, theactuator 300 couples expansion of the polymer 302 in both planardirections 320 and 322 into mechanical output in the direction 320.

Although FIGS. 2A-2K illustrate several actuators suitable for use withmotors of the present invention, other actuators including one or moreelectroactive polymers may also be used. Other exemplary actuatorsinclude bending beam actuators, diaphragm actuators and inchwormactuators are also suitable for use with the present invention.Additional exemplary linear and non-linear actuators suitable for usewith the present invention are described in commonly owned U.S. patentapplication Ser. No. 09/619,848, which was previously incorporated byreference.

5. MOTOR DESIGNS

In general, a motor in accordance with the present invention comprisesone or more electroactive polymers configured in a particular motordesign. The design converts repeated deflection of an electroactivepolymer into continuous rotation of a power shaft included in a motor.There are an abundant number of motor designs suitable for use with thepresent invention—including conventional motor designs retrofitted withone or more electroactive polymers and custom motor designs speciallydesigned for electroactive polymer usage. Several motor designs suitablefor use with the present invention will now be discussed. Theseexemplary rotary motor designs convert deflection of one or moreelectroactive polymers into output rotary motion.

In one aspect, a motor of the present invention comprises one or moreclutches. In general, a clutch allows engagement and disengagementbetween a driving member and a driven member. Most commonly, the drivingmember is coupled to an electroactive polymer transducer and the drivenmember is a power shaft. When engaged, the clutch transmits deflectionand power from the transducer, a portion thereof, or a structureattached thereto, to the power shaft. When disengaged, the clutchprovides disconnection between the transducer and the power shaft. Inother words, when the clutch is disengaged, the transducer may deflectwithout transferring mechanical power to the power shaft.

FIG. 3A illustrates a motor 400 comprising an electroactive polymer inaccordance with one embodiment of the present invention. The motor 400converts electrical power to mechanical power. Motor 400 includes asingle transducer 402 that drives a power shaft 403 using clutch 404.Power shaft 403 is configured to rotate about axis 415, defined bybearings (not shown) that constrain the power shaft 403 in all degreesof freedom except rotation about axis 415.

Transducer 402 comprises electroactive polymer 407 and electrodes 405 aand b deposited on opposing surfaces of polymer 407 (only facingelectrodes 405 is shown). One edge of electroactive polymer 407 isattached to rigid member 406, which is fixed. Rigid member 408 isattached to a central portion of electroactive polymer 407 andtranslates in lateral direction 410. When the left portion ofelectroactive polymer 407 is actuated and expands using electrodes 405a, rigid member 408 deflects linearly in lateral actuation direction 410a. When electroactive polymer 407 is actuated and expands usingelectrodes 405 b, rigid member 408 deflects linearly in lateralactuation direction 410 b. Repeatedly actuating electrode pairs 405 aand b in turn produces reciprocating linear deflection for rigid member408.

Fixed to and orthogonally extending from the rigid member 408 is a rigidmember 409 that includes rack 412 on one surface. Rack 412 meshes withpinion 414 circumferentially disposed on clutch 404. Together, theclutch 404, rack 412 and pinion 414 convert reciprocating lineardeflection of transducer 402 into a single direction of rotation forpower shaft 403. When engaged, clutch 404 transmits linear deflection inthe lateral direction 410 a of rigid member 409 into clockwise rotationof power shaft 403. When disengaged, clutch 404 provides disconnectionbetween rack 412 and output shaft 403 for deflection of rigid member 409in linear return direction 410 b, thus producing no counterclockwiserotation of power shaft 403. Correspondingly, when clutch 404 isdisengaged, electroactive polymer 407 elastically contracts withouttransferring mechanical energy to output shaft 403. A clutch suitablefor use with the present invention includes p/n NRC-4 as provided byBerg, Inc. of East Rockaway, N.Y.

Since the motor 400 comprises only one clutch that rectifies transducer402 deflection to produce clockwise rotation of power shaft 403, itderives rotary output only from lateral actuation direction 410 a. Thus,there is no mechanical energy transferred to the power shaft 403 on theelastic return stroke when clutch 404 is disengaged. To capturemechanical energy produced during elastic return of the polymer,multiple clutches may be used. More specifically, a first clutch mayengage the power shaft for actuation of the polymer and a second clutchengages the power shaft during elastic return of the power shaft.Multiple clutches for the same motor may be useful, for example, whenviscoelastic losses in a motor are significant and any elastic energyavailable from elastic return of a polymer is substantially lost betweenactuations. Multiple clutches may also be useful when the motor isoperating slowly compared to resonance of the electroactive polymer(s)included therein. In this case, even for an electroactive polymer withlow losses, slow actuation of the electroactive polymer allows polymermaterial to lose the elastic return energy since the material will havetime to make many energy-wasting vibrations between actuations.

Multiple clutches are also useful in transmitting deflection and powerfrom multiple transducers and active areas to a single power shaft,particularly when the transducers and active areas actuate out of phasefrom each other or have different primary directions of actuation. FIGS.3B and 3C illustrate a simplified top view and side view, respectively,of a two clutch motor 420 in accordance with another embodiment of thepresent invention. The motor 420 includes two transducers 422 and 424 intension with respect to each other that drive a motor power shaft 426using clutches 428 and 430. Power shaft 426 rotates about a fixed axis425. Transducer 422 comprises electroactive polymer 427 and electrodes435 a and 435 b deposited on opposing surfaces of polymer 427.Transducer 424 comprises electroactive polymer 429 and electrodes 441 aand 441 b deposited on opposing surfaces of polymer 429. Opposite edgesof transducers 422 are attached to rigid members 431 and 432,respectively. Opposite edges of electroactive polymer 424 are attachedto rigid members 436 and 438. Rigid members 431 and 436 are fixed.

Transducers 422 and 424 each deflect in lateral directions 434 and 440.More specifically, when actuated using electrodes 435, rigid member 432deflects linearly in lateral direction 434. Upon removal of theactuation voltage from electrodes 435, elastic restoring forces in theelectroactive polymer 422 deflect rigid member 432 in direction 440.Similarly, when actuated using electrodes 441, rigid member 438 deflectslinearly in direction 440. Upon removal of the actuation voltage fromelectrodes 441, elastic restoring forces in the electroactive polymer429 deflect the rigid member 438 in lateral direction 434.

Clutches 428 and 430 convert deflection of transducers 422 and 424 intoa single direction of rotation for power shaft 426. Clutches 428 and 430are arranged such that their engagement rotates power shaft 426 in thesame direction (clockwise as shown in FIG. 3B). Clutch 428 transmitslinear deflection in the lateral direction 434 into clockwise rotationof power shaft 426. Clutch 430 transmits linear deflection in thelateral direction 440 into clockwise rotation of power shaft 426.Clutches 428 and 430 also allow disengagement between the power shaft426 and the transducers 422 and 424 in the opposite direction ofrotation (counterclockwise).

Cables 433 and 435 transmit linear deflection of the rigid bars 432 and438 to the clutches 428 and 430. Cable 433 is attached to rigid bar 432,extends circumferentially around clutch 428, and is attached to therigid bar 438. Together, clutch 428 (when engaged) and cable 433transmit deflection in lateral direction 434 into clockwise rotation ofshaft 426 for both actuation of transducer 422 and elastic contractionof polymer 429. Cable 435 is attached to rigid bar 432, extends aroundclutch 430, and is attached to rigid bar 438. Together, clutch 430 (whenengaged) and cable 435 transmit deflection in lateral direction 440 intoclockwise rotation of shaft 426 for both actuation of transducer 424 andelastic contraction of polymer 427. In one embodiment, cables 433 and435 are fixed to the clutches 428 and 430 with suitable allowance fortransducer stroke length. As shown in FIG. 4C, cables 433 and 435 areextend circumferentially around clutches 428 and 430 and rely onfriction for power transmission between the cables and power shaft 426.Cable guides 437 are included on top and bottom surfaces of clutch 428to keep cable 433 from slipping axially from clutch 428.

As transducers 422 and 424 actuate in opposing linear directions,clutches 428 and 430 are operably coupled, via cables 433 and 435, tothe output of transducers 422 and 424 such that one clutch is alwaysengaging the output shaft 426 when one of the transducers is beingactuated. Typically, transducers 422 and 424 are actuated out of phasefrom each other. More specifically, transducer 422 is actuated whenvoltage is removed from transducer 424 and transducer 424 is actuatedwhen voltage is removed from transducer 422.

In some applications, it is important to maintain a substantially smoothand continuous output force for power shaft 426. With the two transducermotor 420 of FIG. 3B, some disruption in output force may occur whenswitching between actuation of the two transducers 422 and 424. Forexample, there may be minimal mechanical backlash in clutches 428 and430 as well as delay in electrical switching, either of which may leadto disruption of smooth and continuous output force. In these cases, itmay be desirable to include more than two electroactive polymers.

FIG. 3D illustrates a simplified top view of a multiple clutch motor 445including four transducers in accordance with another embodiment of thepresent invention. The motor 445 includes four orthogonally arrangedtransducers 447 a-d that drive a power shaft 448 using four clutches 446(only facing clutch 446 a is shown). The four clutches 446 convertreciprocating linear deflection of transducers 447 a-d into a singledirection of rotation for power shaft 448. Each set of opposingtransducers has a pair of clutches 446 that transmit transducerdeflection in both linear directions to rotation of power shaft 448. Forexample, transducers 447 b and 447 d are coupled to a pair of clutchesattached to power shaft 448 as illustrated in FIG. 3C. The pair ofclutches operate similar to clutches 428 and 430 described above withrespect to FIGS. 3B and 3C and are not detailed for sale of brevity.Transducers 447 a-d provide actuated deflection in linear orthogonaldirections 449 a-d, respectively. For each transducer, removal of theactuation voltage results in elastic recovery deflection in the oppositedirection as actuation.

Transducers 447 a-d are sequentially fired in a timely manner to producea smooth output force for power shaft 448. As the transducers 447 a-dactuate in opposing directions, the clutches 446 are coupled such thatone clutch always engages power shaft 448 when one of the transducers isbeing actuated. Typically, transducer 447 a is actuated when voltage isremoved from transducer 447 c and transducer 447 b is actuated when thevoltage is removed from transducer 447 d. The timing of transducers 447a and 447 c may then be offset accordingly to produce a smooth outputforce for power shaft 448. In a specific embodiment, actuation of oneset of opposing transducers is timed to be at peak force in actuationstroke when the other set of opposing transducers 447 a-d is beingelectronically switched. In this manner, a smoother output force ismaintained for the output shaft 448 that minimizes disruption in outputforce resulting from electronic switching delays to any of polymers andany mechanical backlash in the clutches 446.

Motors of the present invention may also comprise a monolithictransducer that provides power to rotate a power shaft. In this case,multiple active areas of the monolithic transducer provide independentforces for rotating the power shaft.

FIGS. 3E and 3F illustrate a front view and a top view, respectively, ofa motor 500 in accordance with one embodiment of the present invention.Motor 500 comprises a monolithic transducer 502 similar to actuator 270of FIG. 2I to drive a power shaft 512, using multiple clutches 504 and506.

Translation member 505 includes a central portion 505 c and rigid bars505 a and 505 b that extend from central portion 505 c, which isattached to the center of polymer 507. Translation member 505 providesdisplacement corresponding to deflection of polymer 507. Compliantelectrode pairs 509 and 510 are patterned on both surfaces of polymer507 on either side of rigid bar 505. When electrode pair 507 isactuated, translation member 505 moves in direction 508. Conversely,when electrode pair 509 is actuated, translation member 505 moves indirection 513. Alternating actuation of the electrodes 507 and 509provides a total stroke 514 for translation member 505.

Clutch 504 transmits mechanical energy from monolithic transducer 502 topower shaft 512 in direction 508. Thus, engagement of clutch 504produces rotation of power shaft 512 in a clockwise rotational directionfor actuation using electrodes 507 and rigid bar 505 a movement to theright. Clutch 506 transmits mechanical energy from monolithic transducer502 to power shaft 512 in direction 513. Thus, engagement of clutch 506produces rotation of power shaft 512 in same clockwise direction asclutch 504, but for an opposite direction of deflection of monolithictransducer 502 corresponding to actuation using electrodes 509 and rigidbar 505 b movement to the left. Thus, clutch 504 disengages when clutch506 engages, and vice versa.

FIG. 3G illustrates a simplified front view of motor 520 in accordancewith another embodiment of the present invention. Motor 520 includes aslot 522 having rigid boundaries attached to a monolithic transducer 524and attached to top rigid bar 526 a and bottom rigid bar 526 b. Eachrigid bar 526 has an end attached to the polymer as shown and an endslideably coupled to the rigid boundaries of slot 522. Slot 522 allowstransducer 524 to deflect laterally without interfering with power shaft528. Transducer 524 is fixed on its perimeter to rigid frame 525, whichis included in a housing that supports the components of motor 520. Thehousing also supports power shaft 528, fixing it laterally and allowingit to rotate freely, e.g., using suitable bearings attached to thehousing.

Two clutches 530 are attached to power shaft 528 (only facing clutch 530is shown). Cables 532 are attached to opposite sides of slot 522 andwrap around clutches 530. Together, clutches 530 and cables 532translate power between transducer 524 and power shaft 528 for bothlateral directions of transducer 524 deflection. Cables 532, clutches530, and power shaft 528 are configured similar to the two clutch andcable system of FIGS. 3B and 3C. In this case however, the cables areattached to opposite sides of slot 522 instead of separate transducers422 and 424. Clutches 530 are preferably located on either side oftransducer 524 and positioned as close as possible to the plane oftransducer 524 to prevent twisting of electoactive polymer 529 includedin transducer 524.

Upon actuation of electrode pair 534, rigid bar 526 and the attachedslot 522 translate laterally to the left. As rigid bar 526 translateslaterally to the left, cables 532 rotate both clutches 530. One clutchengages for motion to the left and rotates power shaft 528. Similarly,as rigid bar 526 translates laterally to the right, the other clutch 530engages and rotates power shaft 528 in the same direction.

FIG. 3H illustrates a perspective view of motor 540 in accordance withanother embodiment of the present invention. Motor 540 includes twoactuators 542 and 544 that provide power to a power shaft 546. Actuators542 and 544 are similar to those described in FIGS. 2J and 2K and eachprovide vertical linear output when actuated. Power shaft 546 is rotablysupported by bearings 548 that are included in housing 550. Power shaft546 also includes a widened portion 547 attached on opposite sides tothe upper stiff members included in actuators 542 and 544. Widenedportion 547 acts as a lever for actuator 542 and 544 deflection aboutpower shaft 546.

Actuation of actuator 542 causes power shaft 546 to rotatecounterclockwise. A clutch 552 engages for counterclockwise rotation ofpower shaft 546 and causes wheel 559 to rotate counterclockwise. Whenactuation of actuator 542 is finished, actuation of actuator 544 begins.Together, actuation of actuator 544 and elastic return of theelectroactive polymer included in actuator 542 rotate power shaft 546clockwise. Clutch 552 disengages for clockwise rotation of power shaft546. In this case, wheel 559 maintains enough counterclockwise momentumfrom the initial rotation of power shaft 546 to keep moving duringactuation of actuator 544. When actuation of actuator 544 is finished,actuation of actuator 542 begins. Together, actuation of actuator 542and elastic return of electroactive polymer included in actuator 544rotate power shaft 546 counterclockwise. Again, clutch 552 engages forcounterclockwise rotation of shaft 546 and adds power to thecounterclockwise motion of wheel 559.

To improve consistent power output of motor 540, a mechanism is used toassist output. In this case, wheel 559 acts as a flywheel. Wheel 559stores rotational energy during power impulses of actuator 542 andreleases this energy between power impulses, thus assuring lessfluctuation in motor 540 power and/or speed and smoother motoroperation. The size of wheel 559 will vary with the general constructionand implementation of motor 540. Alternatively, wheel 559 is useful whena load attached to motor 540 is changing in force. In this case, wheel559 helps smooth out the speed variations introduced by the loadvariations.

FIGS. 3I and 3J illustrate a front view and a side perspective view,respectively, of a motor 560 comprising a plurality of active areas on amonolithic transducer in accordance with one embodiment of the presentinvention. Motor 560 includes a monolithic transducer comprising fouractive areas 562 a-d symmetrically arranged around a center point of themonolithic transducer. Crank pin 568 is attached to a crank arm 565 thattransmits force between the crank pin 568 and power shaft 563. Themonolithic transducer deflects crank pin 568 along a circular path 569,thus rotating power shaft 563. The center point of circular path 569corresponds to the center point of the monolithic transducer as well asthe center point and axis of rotation for the power shaft 563.

Each of the active areas 562 a-d includes top and bottom electrodes 564a-d attached to a polymer 561 on its top and bottom surfacesrespectively (only the electrodes 564 a-d on the facing surface of thepolymer 561 are illustrated). The electrodes 564 a-d each provide avoltage difference across a portion of the polymer 561. A first activearea 562 a is formed with the two first active area electrodes 564 a anda first portion 561 a of the electroactive polymer. Similarly, a secondactive area 562 c is formed with the two second active area electrodes564 c and a second portion of the electroactive polymer 561 c. A similararrangement applies to the active areas 562 b and 562 d.

The electrodes 564 a-d and their corresponding active areas 562 a-d aresymmetrically and radially arranged the center point of circular path569 and power shaft 563. Correspondingly, the elasticity of the activeareas 562 a-d is balanced about power shaft 563. As will be describedbelow, the circular path 569 corresponds to a path of substantiallyconstant elastic potential energy for the monolithic transducer of FIG.3I.

A substantially rigid frame 567 is fixed to the perimeter of thecircular polymer 561 using an adhesive. Crank pin 568 is attached to acentral portion of polymer 561. Crank pin 568 deflection relative to therigid frame 567 is thus guided by deflection of the central portion.Crank pin 568 thus deflects via the central portion as determined byactuation of active areas 562 a-d. In some cases, the offset of thecrank (the distance from the central axis of the power shaft 563 to thecenter of the crank pin 568) is smaller for polymers that deflect less,and can be larger for polymers that deflect more.

Actuation of the active area 562 a moves crank pin 568 down. Actuationof the active area 562 b moves crank pin 568 to the left. Actuation ofthe active area 562 c moves crank pin 568 up. Actuation of the activearea 562 d moves crank pin 568 to the right. The active areas 562 arearranged relative to each other such that elastic energy of one activearea facilitates deflection of another. The active area 562 a isarranged relative to the active areas 562 c such that elastic energy ofthe active area 562 a may facilitate deflection of the active area 562c. In this case, contraction of the active area 562 a at least partiallyfacilitates expansion of the active area 562 c, and vice versa. Morespecifically, deflection of the active area 562 a includes a directionof contraction that is at least partially linearly aligned with adirection of expansion for the active area 562 c towards the active area562 a. In another embodiment, the active areas 562 a-d are not groupedinto opposing pairs. In order for the elastic energy of one active areato facilitate the deflection of another active area, it may only benecessary for the active areas share motion in a common lineardirection. In this way the polymer of transducer 560 could have two,three, five or any number of active areas arranged such that the motionof one active area shares a direction with that of another area.

Active areas 562 a-d may be actuated sequentially to repeatedly movecrank pin 568 along a portion 572 of the circular path 569. To achievethis, the active areas 562 a-d are actuated sequentially in a timelymanner. For example, crank pin 568 may begin at the position as shown inFIG. 3I. Electrical energy is then supplied to electrodes 564 d whileactive area 562 b elastically contracts; forcing crank pin 568 to rotateclockwise. After crank pin 568 rotates clockwise past its furthestposition from active area 564 c (a vertical position as shown),electrical energy is then supplied to electrodes 564 a while active area562 c elastically contracts, thus moving crankpin 568 further clockwise.

Clockwise motion of crankpin 568 provides clockwise rotation of powershaft 563. A clutch 571 engages for clockwise rotation of power shaft563 and transmits power from power shaft 563 to a wheel 570 forclockwise rotation of power shaft 563. Clutch 571 disengages wheel 570from power shaft 563 for counterclockwise rotation of power shaft 563.

At the extended position 573, shown by dotted lines in FIG. 3I, activeareas 562 a-d stop clockwise rotation of crankpin 563 and startcounterclockwise rotation thereof. More specifically, electrical energyis supplied to electrodes 564 b while active area 562 d elasticallycontracts, forcing crankpin 568 to rotate counterclockwise. After crankpin 568 rotates clockwise past its furthest position from active area564 c (a vertical position as shown), electrical energy is then suppliedto electrodes 564 a while active area 562 c elastically contracts, thusmoving crankpin 568 further counterclockwise. When the crankpin 568reaches its starting position as shown, active areas 562 a-d stopcounterclockwise rotation of crankpin 563 and repeat clockwise rotationthereof.

Clockwise and counterclockwise motion of crank pin 568 along portion 572of circular path 569 may then the repeatedly continued. Clutch 571 thenrectifies this continuous motion to produce clockwise output of wheel570. Similar to the wheel 559 of FIG. 3H, wheel 570 acts as a flywheelto maintain clockwise motion of wheel 570 between power impulsesprovided by active areas 562 a-d, thus assuring less fluctuation inmotor 540 power and/or speed and smoother motor operation.

6. ENERGY FEATURES

Electroactive polymer material provides a spring force duringdeflection. Typically, polymer material resists deflection duringactuation because of the net increase (counting active and inactiveareas) in elastic energy. Removal of the actuation voltage and theinduced charge causes the reverse effects. In general, when actuationvoltages and any external loads are removed, electroactive polymers, orportions thereof, elastically return to their resting position. In oneaspect of the present invention, elastic properties of one or moreportions of an electroactive polymer, and any energy contribution ofexternal loads, are used to assist power shaft rotation.

In one embodiment, a motor of the present invention is arranged suchthat deflection of a polymer in response to a change in electric fieldis at least partially assisted by mechanical input energy. As the termis used herein, mechanical input energy refers to mechanical energy thatcontributes to deflection of a portion of an electroactive polymer. Themechanical input energy provided to a portion of an electroactivepolymer may include elastic energy provided by another portion of theelectroactive polymer, a portion of another electroactive polymer, aspring, etc. The mechanical input energy may also include energyprovided an external load or mechanism coupled to the electroactivepolymer, e.g, a flywheel coupled to a power shaft. The energy may alsobe provided without using a separate device, for example by exploitingthe rotational energy stored in the shaft or by exploiting the inertialenergy of the polymer mass or connection mass(es).

Cumulatively, the sum of elastic energy in a transducer or motor at agiven instant of time may be referred to as the elastic potential energyof the transducer or motor. Elastic potential energy may be used todescribe transducers and motors of the present invention and methods ofdeflecting these transducers and motors. In one embodiment, a motor isarranged such that deflection of an electroactive polymer issubstantially independent of elastic potential energy. In this case,changes in elastic energy of one or more portions of an electroactivepolymer are balanced by the changes in elastic energy in the remainderof the transducer or motor. Since the deflection does not cause asubstantial change in the net elastic potential energy, the deflectioncan be made with relatively little input electrical energy, even thoughthe individual elastic forces internal to the transducer or motor mightbe relatively larger. Mechanical input energy and substantiallyindependent elastic potential energy deflection are described in furtherdetail in copending U.S. Pat. No. 6,911,764, which is incorporated byreference for all purposes.

The motor 560 of FIG. 3I may be used to demonstrate mechanical inputenergy and substantially constant elastic energy deflection inaccordance with one embodiment of the present invention. The motor 560includes an equipotential line corresponding to the circular path 569assuming the crank pin 568 is initially connected to the exact center ofthe film in its relaxed state, then deflected to path 569. When theactive areas 562 move the crank pin 568 along circular path 569, elasticpotential energy of the motor 560 is substantially independent of theposition of the crank pin 568 on circular path 569. In other words, theelastic potential energy of the motor 560 remains substantially constantas the crank pin 568 moves along circular path 569. This is apparentbecause if the crank pin 568 is initially connected to the center of therelaxed film, then any point along circular path 569 corresponds to thesame deflection of the relaxed center, just in different directions.Since the film is symmetric, the deflection of the pin 568 about thecenter in one direction will yield approximately the same total elasticenergy as a similar deflection about the center in a differentdirection. The elastic energy would be exactly the same for a perfectlyelastic film, but creep and other non-linear effects make the equalityonly approximate. As a result of this elastic energy balance, electricalinput used for actuation of the motor 560 does not need to overcomeelastic energy of the polymer 561 as the crank pin 568 moves alongcircular path 569.

In one embodiment, the crank of motor 560 is a substantially loss-lessmotion constraint that constrains the deflection of the crank pin 568along circular path 569. The rigid motion constraint provides thenecessary forces perpendicular to circular path 569 at any given pointto offset the elastic forces in that direction.

Deflection of the motor 560 includes mechanical input energy fromdifferent portions of the polymer 561. The mechanical input energyincludes elastic energy contributions provided by contractions andexpansions of each of the active areas 562 and portions of the polymer561 outside the active areas 562. A motion constraint such as crank 565does not provide any mechanical input energy by itself, but it providesmechanical forces perpendicular to motion on an equipotential elasticenergy line to assist actuation by holding the motion to a path ofsubstantially constant elastic energy, and thereby eliminate the needfor the expansion and contraction of the polymer to provide theseforces. The amount of mechanical input energy and timing of actuationmay vary. In one embodiment, the total mechanical input energy providedby different portions of the polymer 561 is substantially equal to theelastic energy required to deflect the first active area 562 a for apart of the deflection. In another embodiment, the total mechanicalinput energy provided by different portions of the polymer 561 issubstantially equal to the elastic energy required to deflect the firstactive area 562 a for an entire deflection corresponding to an actuationof one of the active areas 562.

For deflection along circular path 569, the change in total elasticenergy for stretching portions of the polymer 561 during actuation ofone or more of the active areas 562 a-d is substantially equal to thechange in magnitude of the total elastic energy of contracting portionsof the polymer 561. With the elastic energy balanced between thedifferent portions of the polymer 561 along circular path 569, themechanical output energy for motor 560 is greater for a given inputvoltage compared to an arrangement where the elastic energy is notbalanced. In addition, an external load (e.g., the flywheel describedabove) coupled to crank pin 568 may also assist the crank pin 568 toprovide an alternate source of energy to overcome changes in elasticenergy. The flywheel can add or subtract the energy needed to make pin568 move around circlular path 569 in spite of small changes in elasticenergy, and thus reduce the amount of elastic energy that needs to beprovided by electrical actuation of the polymer.

An active area may include multiple directions of contraction andexpansion. Correspondingly, elastic energy generated during actuation ofone active area may used to facilitate deflection of more than one otheractive area. For motor 560, active areas 562 are arranged relative toeach other such that elastic return of one active area 562 a-d mayfacilitate deflection of more than one other active area 562 a-d in adirection of actuation. More specifically, active areas 562 a and 562 care arranged such that contraction of the active area 562 a mayfacilitate expansion of the active area 562 c in a direction towards theactive area 562 a. In addition, active areas 562 a and 562 b arearranged such that contraction of the active area 562 a may facilitateexpansion of the active area 562 b in a direction towards the activearea 562 a.

The timing of deflection between active areas may affect elastic energytransfer therebetween. To increase elastic energy transfer for the motor560, the active areas 561 a-d may be actuated at a high enough rate suchthat elastic return of one active area assists the deflection of morethan one active area subsequently actuated. This may be useful foractive areas having more than one direction of actuation. For example,to increase elastic energy transfer to the active areas 562 b and 561 c,actuation of active areas 562 b and 561 c may begin actuation duringelastic return of active area 561 a. In this manner, elastic energygenerated during actuation of active area 562 a is transferred to twoactive areas 562 b and 562 c actuated thereafter. A similar timing maybe continuously applied as the active areas 562 a-d are actuated inturn.

For the motor 560, there is a complementary nature of the active areas562 a-d on opposite sides of the crank pin 568. It should be noted thatactive areas and transducers for a motor need not be grouped incomplementary pairs as described with the motor 560. For example, an oddnumber of active areas and transducers arranged around the crank pin 568may still employ the elastic energy balance and mechanical input energyfeatures described above. More specifically, three active areas arrangedaround the crank pin 568 at 120 degree intervals may still employ theelastic energy balance and mechanical input energy features describedabove. In this case, the expansion of one active area/transducer ispaired with the contraction of more than one other activearea/transducer.

7. PERFORMANCE

Performance of a motor described herein may be described similar toconventional motor designs by parameters such as force output, poweroutput, weight, efficiency, etc. The performance of motors comprising anelectroactive polymer may also be described with parameters that may notbe present in many conventional motor technologies.

Unlike conventional motor technologies whose power generation elementprovides a constant stroke, it should be noted that electroactivepolymers are capable of providing varying deflection distances andstroke lengths. Thus, when coupled to a clutch and power shaft includedin a motor, a transducer in accordance with the present invention iscapable of varying deflection distances and stroke lengths. Thetransducer may then include a first deflection that rotates the powershaft a first amount corresponding to the first deflection, and a seconddeflection that rotates the power shaft a second amount corresponding tothe second deflection. The second deflection may be greater or less thanthe first deflection and may be used to vary the output of the motor.

Electroactive polymer powered motors may be characterized in terms ofthe motor by itself or the performance of the motor in a specificapplication. Characterizing the performance of a motor by itself mayrelate to the material properties of the polymer included therein aswell as the particular motor design.

As mentioned earlier with respect FIG. 1A, when a polymer expands as aresult of electrostatic forces, it continues to expand until mechanicalforces balance the electrostatic pressure driving the expansion. When aload is attached to a motor of the present invention, mechanical effectsprovided by the load will influence the force balance and deflection ofthe polymer—and thus influence rotation of the output power shaft. Forexample, if the load resists rotational deflection of the power shaft,then the electroactive transducer may not deflect as much as if werethere no load. If the load is too large for the transducers driving thepower shaft, the motor may stall at a stall position. Conventionalelectric motor technologies that rely on moving charge forelectro-mechanical conversion still have current flowing at a stallposition. When left at a stall position for extended periods of time,these conventional electric motor technologies often overheat and damagethe motor. In contrast, electroactive polymer powered motors of thepresent invention rely on electrostatic forces and may not have currentflowing at a stall position. Thus, the power shaft of a motor of thepresent invention may include a stall position that is maintained withsubstantially no electrical current to the electrodes. Thisadvantageously avoids overheating associated with conventional electricmotor motors.

The time for a polymer to rise (or fall) to its maximum (or minimum)actuation pressure is referred to as its response time. Transducers inaccordance with the present invention may accommodate a wide range ofresponse times. Depending on the size and configuration of the polymer,response times may range from about 0.01 milliseconds to 1 second, forexample. A polymer excited at a high rate may also be characterized byan operational frequency. In one embodiment, maximum operationalfrequencies suitable for use with the present invention may be in therange of about 100 Hz to 100 kHz. Thus, motors of the present inventionmay have very good temporal response and control.

In one embodiment, one or more transducers included in a motor areactuated in resonant mode (e.g., the motor 400 of FIG. 3A). Operating anelectroactive polymer at resonance using materials, such as silicone,with low losses (e.g., low viscoelastic losses) allows energy availablefrom the elastic return to stay in the electroactive polymer in the formof resonant mode vibration or kinetic energy for use in a subsequentactuation. In another embodiment, a motor includes a spring thatfacilitates elastic return of the electroactive polymer, e.g., a springthat facilitates elastic return of electroactive polymer 407 in returndirection 410 b. In some cases the clutch can incorporate some amount of“slop” or the ability to free run a little in the driving direction. Inthis case the proportion of energy removed from each stoke is less butthe amplitude and total energy of the motion is greater and thereforethe total energy produced per stroke is greater.

The performance of an electroactive polymer motor as described hereinmay also be adapted using one or more conventional techniques. Forexample, a gear chain may be used to reduce the speed and increase thetorque available from the motor. For applications requiring linearactuation, a rack or ball screw mechanism may convert the high torquerotary motion of an electroactive polymer motor into linear motion. Forexample, a small motor can be attached to lead screw to produce a slowbut high-force and high-stroke linear actuator. More direct methods oflinear motion may also be used. For example, a polymer linear actuatormay be combined with two actuated clamps that can clamp an output shaft.One clamp is located at the “fixed” base of the linear actuator and thesecond is located at the moving end of the actuator. By timing theclamping action of the two clamps relative to the linear actuation ofthe polymer actuator, the shaft can be moved in an “inchworm-type”fashion. Similarly, a linear clutch may be used to rectify theoscillatory motion of a polymer actuator to a constant linear motion inone direction. If the clutch may be electrically engaged and disengaged,and a second such clutch is also included, then by selectively engagingthe proper clutch the output shaft can be moved in either direction.

8. APPLICATIONS

As the present invention includes transducers that may be implemented inboth the micro and macro scales, and with a wide variety of motordesigns, the present invention finds use in a broad range ofapplications where conversion between electrical and mechanical power isrequired. As one of skill in the art will appreciate, there arecountless applications for motors. Broadly speaking, motors of thepresent invention may find use in any application requiring continuousmechanical output. These applications include robotics, pumps,animatronics, etc.

Due to the weight savings gained by using electroactive polymers inproducing mechanical energy for a motor, the present invention iswell-suited for applications that require a light weight motor. Forexample, the present invention is well-suited for applications thatrequire a light weight motor that can operate at low speeds and yetobtain high-performance from the electroactive polymer materials. Thereare countless applications for a light weight, low rpm yet relativelyhigh torque, and efficient motor. In addition, by using high speedelectroactive polymers, the present invention is well-suited forapplications that require a motor that can operate at high speeds andwith low-torque. Further, the light weight gained by using a motorpowered by an electroactive polymer allows improvements to manyapplications where weight of the motor is important to design. Forexample, remote-controlled cars that rely on one or more motors forpower may require less electrical energy to power a lighter vehicle—thusallowing a smaller battery or the same battery to operate for a longerduration.

9. CONCLUSION

While this invention has been described in terms of several preferredembodiments, there are alterations, permutations, and equivalents thatfall within the scope of this invention which have been omitted forbrevity's sake. By way of example, although the present invention hasbeen described in terms of several numerous applied material electrodes,the present invention is not limited to these materials and in somecases may include air as an electrode. In addition, although theexemplary mechanical-electrical power conversion systems described abovewere primarily described with respect to converting electrical tomechanical energy, it is understood that any of these systems may beused in the reverse direction, that is, in converting mechanical powerto electrical power by oscillating the shaft though an angle. It istherefore intended that the scope of the invention should be determinedwith reference to the appended claims.

1. A mechanical-electrical power conversion system comprising: a power shaft configured to rotate about an axis; and at least one transducer mechanically coupled to the power shaft, the at least one transducer comprising a first active area, which includes a first portion of at least one electroactive polymer and two first active area electrodes coupled to the first portion of the at least one electroactive polymer, and a second active area, which includes a second portion of the at least one electroactive polymer and two second active area electrodes coupled to the second portion of the at least one electroactive polymer.
 2. The system of claim 1 wherein the at least one transducer is a monolithic transducer that includes both the first active area and the second active area on a single electroactive polymer.
 3. The system of claim 2 wherein elasticity of the first and second active areas is substantially balanced about power shaft.
 4. The system of claim 1 wherein the power shaft includes a stall position that is maintained with substantially no electrical current to the first active area electrodes and the second active area electrodes.
 5. The system of claim 1 wherein the at least one transducer is mechanically coupled to the power shaft using a crank having a crank pin and a crank arm that transmits force between the crank pin and the power shaft.
 6. The system of claim 5 wherein the at least one transducer includes an actuator.
 7. The system of claim 6 wherein the actuator applies translational motion to the crank pin, which in turn rotates the power shaft to provide power output thereon.
 8. The system of claim 5 wherein deflection of the first active area and the second active area along a path provided by the crank arm is substantially independent of elastic potential energy of the at least one transducer.
 9. The system of claim 1 wherein the at least one transducer includes a second transducer that includes a second electroactive polymer that includes the second active area.
 10. The system of claim 9 wherein elasticity of a first electroactive polymer and elasticity of the second electroactive polymer are balanced about power shaft.
 11. The system of claim 9 wherein the first electroactive polymer and the second electroactive polymer are both monolithic electroactive polymers each having multiple active areas.
 12. The system of claim 11 wherein the active areas of the first monolithic transducer are offset from the active areas of the second monolithic transducer.
 13. The system of claim 1 wherein the system is arranged such that elastic potential energy stored in the second portion of the at least one electroactive polymer during actuation of the second active area at least partially contributes to deflection of the first portion of the at least one electroactive polymer when the first active area is actuated using the first active area electrodes.
 14. The system of claim 1 wherein the first and second active areas are symmetrically arranged about the power shaft.
 15. The system of claim 1 further comprising a support structure for securing the at least one transducer and for directing a mechanical output derived from the at least one transducer.
 16. The system of claim 15 wherein the support structure includes a substantially rigid frame.
 17. The system of claim 1 wherein the at least one electroactive polymer has an elastic modulus at most about 100 MPa.
 18. The system of claim 1 wherein the at least one electroactive polymer is pre-strained by a factor in the range of about 1.5 to about 50 times an original area of the at least one electroactive polymer prior to the pre-strain.
 19. A mechanical-electrical power conversion system comprising: a power shaft configured to rotate about an axis; and at least one transducer mechanically coupled to the power shaft, the at least one transducer comprising a first active area, which includes a first portion of at least one electroactive polymer and first active area electrodes coupled to the first portion of the at least one electroactive polymer, and a second active area, which includes a second portion of the at least one electroactive polymer and two second active area electrodes coupled to the second portion of the at least one electroactive polymer, wherein the system is arranged such that elastic potential energy stored in the second portion of the at least one electroactive polymer during actuation of the second active area at least partially contributes to deflection of the first portion of the at least one electroactive polymer when the first active area is actuated using the two first active area electrodes.
 20. The system of claim 19 wherein the at least one transducer is a monolithic transducer that includes both the first active area and the second active area on a single electroactive polymer. 